Demystifying Hazmat Chemistry

STUDENT HANDOUT
DEMYSTIFYING HAZMAT CHEMISTRY
The values we use most often in emergency response are IDLH and LOC. IDLH (Immediately
Dangerous to Life and Health) means an atmosphere that poses an immediate threat to life, would
cause irreversible adverse health effects, or would impair an individual’s ability to escape from a
dangerous atmosphere.
IDLH values were initially developed as part of a joint project by NIOSH and OSHA as a tool for
selecting respirators in the workplace. As a safety margin, IDLH values were based on effects that
might occur from a 30-minute exposure, but it was not meant to imply that workers should stay
in the environment without proper PPE any longer than necessary. Rather, every effort should be
made to exit immediately. IDLH should be thought of like an SCBA low-air alarm. It’s a window for
escape, not a window for squeezing in additional mitigation measures in the time remaining.
IDLH is often used to distinguish between a rescue and a body recovery operation. If a victim
has been exposed to the product at or above an IDLH concentration for more than 30 minutes,
the chances of survival drop significantly. However, IDLH is only part of the “risk versus gain”
analysis. It is generally not possible to make a positive determination of death from a distance.
IDLH is generally based on toxicological data. However, where flammability is a significantly
greater risk than toxicity, IDLH may be set at 10% of the lower explosive limit (LEL).
LOC (Level of Concern) is the value used to determine the geographic area of risk in the event of
a chemical release. This is generally the point at which evacuation or in-place protection measures
are implemented. LOC is generally defined as 10% of the IDLH. Unlike the other limits,
LOC has no associated description of health effects that might be expected. It is simply a safety
margin of 10%—just like 10% of a lower explosive limit (LEL) provides a safety margin to keep
from entering the flammable range.
LOC is a rough way of setting community exposure limits when one has no other information.
Whenever possible, emergency planning and community protection should be based on one of
the Protective Action Criteria (PAC) values listed below. (See next page for details.)
• Acute Exposure Guideline Levels (AEGL) - (first choice if available)
• Emergency Response Planning Guidelines (ERPG) - (second choice, if no AEGL exists)
• Temporary Emergency Exposure Limits (TEEL) - (third choice, if there is no AEGL or ERPG)
If you can’t find IDLH or LOC in your reference books, you can estimate IDLH or LOC if you know
the TLV-TWA. (See next page.) LOC is generally defined as 10% of the IDLH or 3 times the TLV-
TWA; thus IDLH is 10 times the LOC or 30 times the TLV-TWA. Remember, however, that these
are approximations only.
Shown below is a hazard ladder to plot toxicity, similar to the one used to plot oxygen deficiency.
Later you’ll see how the two can be used together to help assess risk.
A Toxicity Hazard Ladder
0%
Toxicity
IDLH _______________
1%
10,000
ppm
2% 3% 4% 5% 6% 7% 8% 9%
20,000
ppm
30,000
ppm
40,000
ppm
50,000
ppm
60,000
ppm
70,000
ppm
80,000
ppm
90,000
ppm
10% 11% 12% 13%
100,000
ppm 110,000
ppm 120,000
ppm 130,000
ppm
Continuing Challenge 2007 Page 10 © 2007 Firebelle Productions and CHES